Method for feeding an MTG conversion reactor

Abstract

A method of and apparatus for reducing the amount of water in the feed to a methanol-to-gasoline (MTG) conversion reactor is described. The output products of a dehydration reactor and an aqueous methanol feed are supplied to a primary distillation tower or separator. A dimethylether (DME)/methanol mixture is taken as overhead from the primary tower and can be sent to the MTG conversion reactor to produce hydrocarbons boiling in the gasoline range. Bottoms from the primary tower, containing methanol and water, are supplied to a secondary distillation tower or separator. A methanol stream is drawn as overhead from the secondary tower and is passed to an acid catalyzed dehydration reactor where an equilibrium mixture of dimethylether, methanol, and water is produced. The equilibrium mixture is passed from the dehydration reactor to the primary distillation tower. In preferred embodiments, the conversion reactor feed from the primary distillation tower may be of a gaseous or liquid phase.

What is claimed is: 
     
       1. A continuous process for producing an essentially water-free dimethylether-containing feedstream comprising: passing a crude methanol feed containing a minor amount of water to an upper stage of a pressurized primary distillation tower and concurrently passing a dehydration reaction product of dimethylether, methanol, and water from a dehydration reactor to an intermediate stage of the primary distillation tower;   withdrawing from the primary distillation tower an overhead stream of an essentially water-free dimethylether-containing feedstream having a dimethylether to methanol molar ratio of at least about 1.15 to 1 and an aqueous methanol bottoms stream;   conducting the bottoms stream containing aqueous methanol to a secondary distillation tower;   withdrawing from the secondary distillation tower an overhead methanol stream and a bottoms stream of water which is recovered in a collection zone;   passing the secondary overhead methanol stream to a dehydration reactor containing an acid methanol dehydration catalyst; and   withdrawing from the dehydration reactor a dehydration reaction product stream of dimethylether, methanol, and water, which reaction product stream is recycled to the primary distillation tower.   
     
     
       2. The process of claim 1 wherein the overhead stream of an essentially water-free dimethylether-containing feedstream from the primary distillation tower is sent directly to a methanol-to-gasoline conversion reactor containing ZSM-5 catalyst. 
     
     
       3. The process of claim 2 wherein the primary distillation tower is operated at a minimum pressure of at least that of the methanol-to-gasoline conversion reactor. 
     
     
       4. The process of claim 1 wherein the primary distillation tower is operated at a pressure of about 825 to 2040 kPa. 
     
     
       5. A process according to claim 1 wherein the primary distillation tower contains at least twenty theoretical stages. 
     
     
       6. A process according to claim 5 wherein the crude methanol feed enters the primary distillation tower at an upper inlet which is at least two theoretical stages above the intermediate inlet for the reaction product mixture of dimethylether, methanol, and water. 
     
     
       7. A process according to claim 1 wherein the primary distillation tower is operated at a reflux ratio of 1.1 to 3.8. 
     
     
       8. A process according to claim 1 wherein the overhead from the primary distillation tower has a dimethylether to methanol molar ratio of from 1.5:1 to 99:1 and a water content not more than about 1 mole percent. 
     
     
       9. A process according to claim 1 wherein the crude methanol feed contains about 4 to 20 wt. percent water. 
     
     
       10. A continuous method for converting a methanol feedstream to a substantially dewatered mixture consisting essentially of dimethylether and methanol, comprising the steps of distilling the methanol feedstream in a first separation zone concurrently with dehydration reaction effluent to provide an ether rich first overhead stream substantially free of water and an aqueous methanol first liquid bottoms stream;   further distilling the aqeuous methanol stream in a second separation zone to provide a methanol-rich second overhead stream and a second liquid bottoms stream predominately comprising water;   contacting the methanol-rich second overhead stream with an acid dehydration catalyst in a dehydration reaction zone at elevated temperature to convert methanol to dimethylether and water; and passing the dehydration reaction effluent to the first separation zone.   
     
     
       11. A continuous process for producing an essentially water-free dimethylether-containing feedstream for a chemical conversion reactor comprising: passing a crude methanol feed containing a minor amount of water to an upper stage of a pressurized primary distillation tower operated at a minimum pressure of at least that of the chemical conversion reactor and concurrently passing a dehydration reaction product of dimethylether, methanol, and water from a dehydration reactor to an intermediate stage of the primary distillation tower;   withdrawing from the primary distillation tower an overhead stream of an essentially water-free dimethylether-containing feedstream having a dimethylether to methanol molar ratio of at least about 1.15 to 1 and an aqueous methanol bottoms stream;   conducting the overhead stream of the dimethylether-containing feedstream from the primary distillation tower to a chemical conversion reactor;   conducting the bottoms stream containing aqueous methanol to a secondary distillation tower;   withdrawing from the secondary distillation tower an overhead methanol stream and a bottoms stream of water which is recovered in a collection zone;   passing the secondary overhead methanol stream to a dehydration reactor containing an acid methanol dehydration catalyst; and   withdrawing from the dehydration reactor a dehydration reaction product stream of dimethylether, methanol, and water, which reaction product stream is recycled to the primary distillation tower.